A common method for the manufacture of asphalt shingles is the production of a continuous strip of asphaltic shingle material followed by a shingle cutting operation which cuts the material into individual shingles. In the production of asphaltic strip material, either an organic felt or a glass fiber mat has passed through a coater, containing liquid asphalt at a very hot temperature, to form a tacky coated asphaltic strip. Subsequently, the hot asphaltic strip is passed beneath one or more granule applicators which apply the protective surface granules to portions of the asphaltic strip material. Typically, the granules are dispensed from a hopper at a rate which can be controlled by making manual adjustments on the hopper. In the manufacture of colored shingles, two types of granules are employed. Headlap granules are granules of relatively lower cost for portions of the shingle which are to be covered up. Colored granules are of relatively higher cost and are applied to the portion of the shingle which will be exposed on the roof. A typical shingle manufacturing process continuously manufactures the shingle material in a width sufficient for cutting the material into three shingles.
Not all of the granules applied to the hot, tacky, coated asphaltic strip adhere to the strip, and, typically, the strip material is turned around a slate drum to invert the strip and cause the non-adhered granules to drop off. These non-adhered granules, which are known as backfall granules, are usually collected in a backfall hopper. The backfall granules are discharged at a set rate from the backfall hopper onto the strip material.
One of the problems associated with such granule application procedures is that there is no control, other then manual control, of the rate at which the granules are discharged from the headlap hopper, the colored granule hopper, and the backfall hopper. Also, in the event too many or too few granules are being discharged from the headlap hopper or the colored granule hopper, there is no method or means for correcting that condition other than human observation.
The present invention solves the above problem by providing means for sensing the amount of non-adhered granules and controlling the application of granules in response to the sensed amount of non-adhered granules.